China has announced it is investigating a man who used to be one of the country's most powerful politicians, former domestic security chief Zhou Yongkang. The investigation is likely to boost already growing public support for Chinese President Xi Jinping's widening anti-corruption drive.

A brief announcement of the decision came late Tuesday from China's Xinhua news agency. In its report, Xinhua said the party's top investigating body, the Central Commission for Discipline Inspection, had begun an investigation into Zhou Yongkang's suspected "serious disciplinary" violations.

Hong Kong University of Science and Technology political scientist David Zweig says the decision to go after Zhou is perhaps the biggest investigation since the Gang of Four at the end of the Cultural Revolution.

"This is a big deal and many, many people would worry that if you can go after people, you know members of the politburo standing committee after they stepped down, than many many [other] people would be vulnerable," Zweig said.

For months, China has been anticipating the announcement of an investigation into Zhou Yongkang.

Since late last year there have been numerous unconfirmed reports in foreign media that Zhou was the focus of a corruption probe. But when an official announcement did not come in March when the Communist Party held top-level meetings in Beijing, some began to question Chinese President Xi Jinping's commitment to stamping out corruption.

The Communist Party says it is in a life or death struggle against corruption - a problem that not only threatens the party and state, but also prospects for much needed reform.

Zweig says that while Xi most likely needed to get a lot of people to agree with the decision to go forward with the investigation, it is easy to understand why it is necessary. Zhou is a classic example of someone who had too much power, he says.

"He had so much political and legal power being the head of the legal affairs leadership group of the Communist Party, he just was an enormous powerful position to be able to do what he wanted, when you got that kind of power over police courts, who gets shot, who gets executed that is just an enormous amount of power in a totally un-transparent system," he said.

Although the announcement of the party's investigation into Zhou marks a big step forward, it is not necessarily a guarantee that he could face criminal charges, says Hong Kong Baptist University political scientist Jean-Pierre Cabestan.

"In China it is up to the party whether a case should be transferred to the judiciary or should be dealt with within the party apparatus," Cabestan explained. " If there are serious crimes suspected to having been committed by Zhou Yongkang, which is likely, the case will probably be transferred to the judiciary, if not this will be dealt with within the party."

Since taking over as China's leader, President Xi has carried out a highly publicized crackdown on government corruption. Zhou is a close ally of former rising political star Bo Xilai, who was sentenced to life in jail last year.

The anti-corruption drive has won Mr. Xi much praise, but some are also concerned it is just political infighting.

"I think there is a lot of cynicism around, so a lot of Chinese know it very well, it is also a political case and it is not going to accelerate reform or let alone political change in China," Cabestan said. "What they see is that Xi Jinping is getting more and more powerful and is centralizing power in his own hands, for the better or maybe for the worse."

Zhou rose up within China's ranks serving in several key posts that contributed to his power and influence and that are also likely to be key focuses of the corruption investigation. He previously served as the head of the state-owned China National Petroleum Corporation and as a Sichuan provincial party secretary. Sichuan province and CNPC have already been shaken by corruption investigations, many into individuals closely linked to Zhou.

While Zhou served as China's security chief, overseeing domestic intelligence, paramilitary police, judges and prosecutors, the country's domestic security budget began outpacing spending for national defense.